Etching method, etching apparatus, and method for manufacturing semiconductor device

ABSTRACT

In order to reliably remove, by wet etching, a compound containing a metal and silicon, e.g., a silicate ( 101   a ) containing hafnium metal, the silicate ( 101   a ) is oxidized and then the oxidized silicate ( 101   a ) is wet-etched.

TECHNICAL FIELD

The present invention relates to a method and apparatus for removing, bywet etching, a compound containing a metal such as hafnium and silicon,and a method for manufacturing a semiconductor device using the same.

BACKGROUND ART

In recent years, it has been proposed in the art to use a highdielectric constant material (hereinafter referred to as a “high-kmaterial”) in the gate insulating film of a field-effect transistor inorder to prevent the decrease in the driving current while suppressingthe increase in the gate current. Specifically, it has been proposed inthe art to use hafnium oxide (HfO₂: relative dielectric constant ε=30),zirconium oxide (ZrO₂: relative dielectric constant ε=25), or the like,as the material of the gate insulating film so as to maintain a desiredthickness of the gate insulating film, thereby reducing the leak current(see, for example, Japanese Laid-Open Patent Publication No.2000-49349).

When hafnium oxide, for example, is used as the material of the gateinsulating film, a silicate (hafnium silicon oxide) is formed at theinterface between the silicon substrate and the gate insulating film.Specifically, when a heat treatment is performed after a gate insulatingfilm made of a high-k material such as hafnium oxide or zirconium oxideis formed on a silicon substrate, the gate insulating film reacts withthe underlying silicon substrate, whereby an insufficiently-oxidizedsilicate, which is a compound between the material of the gateinsulating film and silicon, is formed near the surface of the siliconsubstrate. Where a hafnium oxide film is used as the gate insulatingfilm, insufficiently-oxidized hafnium silicon oxide is formed as thesilicate. Moreover, where a zirconium oxide film is used as the gateinsulating film, insufficiently-oxidized zirconium silicon oxide isformed as the silicate.

Wet etching using an aqueous hydrogen fluoride solution is suitable foretching away a hafnium oxide film, a zirconium oxide film, or the like,as with a silicon oxide film. This is because an aqueous hydrogenfluoride solution does not substantially etch the silicon substrate.

However, it is difficult to remove a silicate such as hafnium siliconoxide or zirconium silicon oxide by a wet etching method using hydrogenfluoride, or the like. Specifically, the etching rate of wet etchingusing hydrogen fluoride, or the like, for hafnium silicon oxide orzirconium silicon oxide is about 1/10 to 1/30 that for hafnium oxide orzirconium oxide. Thus, when an insulative metal oxide film such as ahafnium oxide film is used as the gate insulating film, aninsufficiently-oxidized silicate layer such as a hafnium silicon oxidefilm is formed at the interface between the silicon substrate and thegate insulating film, and it is difficult to remove the silicate layerby a wet etching method using hydrogen fluoride, or the like. As aresult, the unremoved silicate remains on the surface of the siliconsubstrate when forming the gate electrode structure. Thus, a pluralityof minute field-effect transistors, which are supposed to beelectrically separated from one another, are electrically shorted withone another. Moreover, through a heat treatment step after the formationof the gate electrode structure, the silicate remaining on the surfaceof the silicon substrate is implanted into the silicon substrate as animpurity, thereby forming a level due to the impurity, which adverselyinfluences the semiconductor substrate.

DISCLOSURE OF THE INVENTION

In view of the above, it is an object of the present invention to makeit possible to reliably remove, by wet etching, a compound containing atleast a metal and silicon, specifically, an insufficiently-oxidizedsilicate containing a hafnium metal, a zirconium metal, or the like.

In order to achieve the object set forth above, an etching method of thepresent invention includes: a first step of oxidizing a compoundcontaining at least a metal and silicon; and a second step of removingthe oxidized compound by wet etching.

With the etching method of the present invention aninsufficiently-oxidized compound containing a metal and silicon isoxidized, whereby the composition of the compound can be brought closerto the stoichiometric composition of the metal oxide. Therefore, theinsufficiently-oxidized compound, which is normally insoluble in anetching liquid (hereinafter referred to as an “etchant”) such as anaqueous hydrogen fluoride solution, is oxidized, and becomes moresoluble in the etchant, whereby it is possible to reliably remove thecompound by wet etching.

In the etching method of the present invention, if the metal to beetched is hafnium or zirconium, the composition of the oxidized compoundis closer to the stoichiometric composition of hafnium oxide (HfO₂) orzirconium oxide (ZrO₂), whereby it is possible to reliably remove theoxidized compound by wet etching using hydrogen fluoride, or the like.

In the etching method of the present invention, if the compound to beetched is an oxygen-containing (insufficiently-oxidized) silicatecompound, the composition of the silicate compound is brought evencloser to the stoichiometric composition of the metal oxide by theoxidization, whereby it is possible to reliably remove the oxidizedsilicate compound by wet etching using hydrogen fluoride, or the like.

In the etching method of the present invention, if the compound to beetched is an intermetallic compound (e.g., a silicide), the compositionof the oxidized intermetallic compound is brought closer to thestoichiometric composition of the metal oxide; whereby it is possible toreliably remove the oxidized intermetallic compound by wet etching usinghydrogen fluoride, or the like.

In the etching method of the present invention, it is preferred that thefirst step includes a step of irradiating the compound with ultravioletlight in an oxygen-containing atmosphere.

In this way, ozone is generated by the ultraviolet light irradiation,whereby the compound can reliably be oxidized by the ozone, startingfrom its surface side.

Moreover, in this case, it is preferred that the ultraviolet lightirradiation is performed while supplying a nitrogen gas into theatmosphere.

In this way, it is possible to suppress the attenuation of ultravioletlight in the atmosphere, whereby ozone can reliably be generated by theultraviolet light irradiation. Moreover, similar effects can be obtainedby using another inert gas, instead of a nitrogen gas.

In the etching method of the present invention, it is preferred that astep of irradiating the compound with ultraviolet light while anoxygen-containing liquid (e.g., water) is attached to a surface of thecompound is included.

In this way, ozone is generated by the ultraviolet light irradiation,whereby the compound can reliably be oxidized by the ozone, startingfrom its surface side.

In the etching method of the present invention, it is preferred that thefirst step includes a step of exposing the compound to anozone-containing solution.

In this way, the compound can reliably be oxidized, starting from itssurface side.

In the etching method of the present invention, it is preferred that asolution containing fluorine and hydrogen is used as an etchant in thesecond step.

In this way, it is possible to reliably remove the oxidized compound bywet etching using a solution containing fluorine and hydrogen,specifically, an aqueous hydrogen fluoride solution.

Moreover, in this case, the solution containing fluorine and hydrogenmay be supplied in a gaseous state.

In the etching method of the present invention, it is preferred that themetal is hafnium or zirconium; and a solution containing fluorine andhydrogen is used as an etchant in the second step.

In this way, by oxidizing an insufficiently-oxidized compound, thecomposition of the compound is brought closer to the stoichiometriccomposition of hafnium oxide (HfO₂) or zirconium oxide (ZrO₂), wherebyit is possible to reliably remove the oxidized compound by wet etchingusing a solution containing fluorine and hydrogen, specifically,hydrogen fluoride.

In the etching method of the present invention, if the compound isformed on a silicon region; and the second step includes a step ofremoving the oxidized compound, thereby exposing the silicon region, thefollowing effect is obtained.

That is, since the oxidized compound is easily dissolved in a solutionsuch as hydrogen fluoride, for example, while the silicon region is noteasily dissolved in the solution, whereby the oxidized compound can beselectively removed by wet etching. Thus, a clean silicon region surfacecan be exposed. Moreover, the etching process can reliably be stopped atthe surface of the silicon region.

Note that in the etching method of the present invention, a set of stepsincluding the first step and the second step may be performedrepeatedly, or the first step and the second step may be performedsimultaneously.

A first etching apparatus of the present invention includes: a table onwhich an etching object is placed; a light source for irradiating theetching object placed on the table with ultraviolet light; and asolution supply section for supplying an etchant to the etching objectplaced on the table.

With the first etching apparatus, in a case where the etching object isa compound containing a metal and silicon, ultraviolet light is radiatedfrom the light source toward the etching object in an oxygen-containingatmosphere, whereby ozone is generated, and the ozone oxidizes theetching object. In this way, the composition of theinsufficiently-oxidized etching object can be brought closer to thestoichiometric composition of the metal oxide, whereby it is possible toreliably remove the etching object by supplying an etchant such ashydrogen fluoride, for example, from the solution supply section to theetching object.

In the first etching apparatus, if the apparatus further includes arotating mechanism for spinning the table, it is possible to uniformlysupply the etchant to the etching object.

In the first etching apparatus, if the apparatus further includes a gassupply section for supplying a nitrogen gas to the etching object placedon the table, it is possible to suppress the attenuation of ultravioletlight, whereby ozone can reliably be generated by the ultraviolet lightirradiation. Moreover, similar effects can be obtained with a gas supplysection supplying another inert gas, instead of a nitrogen gas.

A second etching apparatus of the present invention includes: a table onwhich an etching object is placed; a first solution supply section forsupplying an ozone-containing solution to the etching object placed onthe table; and a second solution supply section for supplying an etchantto the etching object placed on the table.

With the second etching apparatus, in a case where the etching object isa compound containing a metal and silicon, an ozone-containing solutionis supplied to the etching object from the first solution supplysection, whereby the solution oxidizes the etching object. Therefore,the composition of the insufficiently-oxidized etching object can bebrought closer to the stoichiometric composition of the metal oxide,whereby it is possible to reliably remove the etching object bysupplying an etchant such as hydrogen fluoride, for example, from thesecond solution supply section to the etching object.

In the second etching apparatus, if the apparatus further includes arotating mechanism for spinning the table, it is possible to uniformlysupply the etchant to the etching object.

In the second etching apparatus, the apparatus may further include alight source for irradiating the etching object placed on the table withultraviolet light.

A method for manufacturing a semiconductor device of the presentinvention includes: a step of forming a gate insulating film on asilicon region; a step of forming a conductive film on the gateinsulating film; a step of forming a gate electrode by dry-etching theconductive film using a mask that covers a gate electrode formationregion; and a step of removing a portion of the gate insulating filmoutside the gate electrode by wet etching. Moreover, the gate insulatingfilm includes an insulating layer made of a compound containing a metal,silicon and oxygen. Furthermore, the step of removing the gateinsulating film includes a step of oxidizing the insulating layer andthen removing the oxidized insulating layer by wet etching.

With the method for manufacturing a semiconductor device of the presentinvention, a gate insulating film having an insulating layer made of acompound containing a metal, silicon and oxygen, i.e., a silicate layer,is etched by oxidizing the insufficiently-oxidized silicate layer andthen wet-etching the oxidized silicate layer. In this process, thecomposition of the oxidized silicate layer is brought closer to thestoichiometric composition of the metal oxide, whereby the silicatelayer becomes more soluble in an etchant such as an aqueous hydrogenfluoride solution, for example. Thus, it is possible to reliably removethe silicate layer by wet etching. Therefore, it is possible to preventa situation where impurities remain between gate electrode structures,thereby improving the production yield in the manufacture of asemiconductor device.

Moreover, with the method for manufacturing a semiconductor device ofthe present invention, in a case where an aqueous hydrogen fluoridesolution is used as an etchant, the aqueous hydrogen fluoride solutiondoes not substantially etch the silicon region (e.g., a siliconsubstrate) underlying the gate insulating film, whereby it is possibleto selectively etch a silicate containing hafnium, for example.

In the method for manufacturing a semiconductor device of the presentinvention, it is preferred that the metal is hafnium or zirconium; and asolution containing fluorine and hydrogen is used as an etchant in thestep of removing the insulating layer.

In this way, the composition of the oxidized insulating layer is broughtcloser to the stoichiometric composition of hafnium oxide or zirconiumoxide, whereby the insulating layer can reliably be removed by wetetching using a solution containing fluorine and hydrogen, specifically,hydrogen fluoride.

In the method for manufacturing a semiconductor device of the presentinvention, the gate insulating film may further include an oxide filmformed on the insulating layer and made of an oxide of a metal of thesame kind as the metal; and the step of removing the gate insulatingfilm may include a step of removing a portion of the oxide film outsidethe gate electrode by wet etching before oxidizing the insulating layer.It may not be necessary to wait for the insulating layer to be exposedbefore performing the etching method of the present invention, i.e.,before performing the set of processes including the oxidization processand the etching process, to remove the insulating layer. In other words,the set of processes may be initiated to remove the oxide film when theconductive film for forming the gate electrode is removed and the oxidefilm is exposed.

A first compound analysis method of the present invention includes: astep of oxidizing a compound containing at least a metal and silicon; astep of removing the oxidized compound by wet etching while collecting aused etchant; and a step of analyzing the collected etchant to identifyan impurity contained in the compound.

Thus, the first compound analysis method is a compound analysis methodusing the etching method of the present invention. Specifically, thecompound analysis is performed by performing the etching method of thepresent invention on a compound containing a metal and silicon and thencollecting and analyzing the used etchant. Therefore, it is possible toreliably remove a silicate compound, or the like, which is difficult toremove by a conventional wet etching process, and it is possible toeasily identify the impurities contained in the compound simply byanalyzing the collected etchant.

A second compound analysis method of the present invention includes: afirst etching step of removing a first layered film by wet etching whilecollecting a used etchant, the first layered film including alower-layer film made of a compound containing a metal, silicon andoxygen and an upper-layer film formed on the lower-layer film and madeof an oxide of a metal of the same kind as the metal; a first analysisstep of analyzing the etchant collected in the first etching step toidentify an impurity contained in the first layered film; a secondetching step of removing an upper-layer film of a second layered filmhaving the same structure as that of the first layered film by wetetching while collecting a used etchant; a second analysis step ofanalyzing the etchant collected in the second etching step to identifyan impurity contained in the upper-layer film in the second layeredfilm; and a third analysis step of comparing an analysis result from thefirst analysis step and an analysis result from the second analysis stepwith each other to identify an impurity contained in the lower-layerfilm. Moreover, the first etching step includes a step of oxidizing thelower-layer film in the first layered film and then removing theoxidized lower-layer film by wet etching.

Thus, the second compound analysis method is a compound analysis methodusing the etching method of the present invention. Specifically, in acase where the first layered film is removed by wet etching, the etchingmethod of the present invention is performed on the lower-layer film inthe first layered film, i.e., the layer of a compound containing ametal, silicon and oxygen. Therefore, it is possible to reliably removethe first layered film including the lower-layer film by wet etching,whereby it is possible to easily identify the impurities contained inthe first layered film simply by analyzing the collected etchant.Moreover, impurities contained in the upper-layer film are identifiedseparately by using the second layered film having the same structure asthat of the first layered film. Therefore, by comparing theidentification results with those for the impurities in the firstlayered film, it is possible to indirectly identify the impurities inthe lower-layer film, without directly identifying the impuritiescontained in the lower-layer film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) to FIG. 1(d) are cross-sectional views illustrating steps of amethod for manufacturing a semiconductor device according to the firstembodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a configuration of an etchingapparatus according to the first embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating a configuration of an etchingapparatus according to a variation of the first embodiment of thepresent invention.

FIG. 4 shows the results of XPS performed by the present inventor on thestate of chemical bond on the surface of each sample (hafnium silicate)prepared through a different process.

FIG. 5 is a flow chart illustrating a compound analysis method accordingto the second embodiment of the present invention.

FIG. 6 is a diagram illustrating an example of a cross section of asubstrate to which the compound analysis method according to the secondembodiment of the present invention is applied.

FIG. 7 is a diagram illustrating an example of a cross section of asubstrate to which the compound analysis method according to a variationof the second embodiment of the present invention is applied.

FIG. 8 shows the analysis results by the compound analysis methodaccording to the variation of the second embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

A method for manufacturing a semiconductor device according to the firstembodiment of the present invention, specifically, a method formanufacturing a field-effect transistor using a hafnium oxide film asthe gate insulating film, will now be described with reference to thedrawings.

FIG. 1(a) to FIG. 1(d) are cross-sectional views illustrating steps ofthe method for manufacturing a semiconductor device according to thefirst embodiment.

First, as illustrated in FIG. 1(a), a hafnium oxide film 101 having athickness of about 10 nm is formed on a substrate 100 made of silicon,for example, by a CVD (chemical vapor deposition) method or a sputteringmethod, for example. In this process, the hafnium oxide film 101 may beformed on a silicon substrate whose surface has been treated withnitrogen.

Then, as illustrated in FIG. 1(b), a polysilicon film 102 to be the gateelectrode material having a thickness of about 200 nm is deposited onthe hafnium oxide film 101 by, for example, a low-pressure CVD methodusing a silane gas. In this process, the hafnium oxide film 101 reactswith the silicon layer on the surface of the substrate 100 due to thehigh temperature during the deposition of the polysilicon film 102,whereby a hafnium silicate (HfSi_(x)O_(y): x>0, y>0), specifically, ahafnium silicon oxide film 101 a, is formed. Note that not all of thehafnium oxide film 101 is turned into the hafnium silicon oxide film 101a, but the hafnium silicon oxide film 101 a having a thickness dependenton the thickness of the deposited hafnium oxide film 101 is formed nearthe surface of the substrate 100. In the following description, theportion of the hafnium oxide film 101 that is not turned into thehafnium silicon oxide film 101 a will be referred to as a hafnium oxidefilm 101 b. Thus, in the present embodiment, the gate insulating filmhas a layered structure including the hafnium oxide film 101 b and thehafnium silicon oxide film 101 a. Note that where the hafnium oxide film101 is formed after nitriding the surface of the substrate 100, i.e., asilicon substrate, a hafnium nitride silicon oxide film, instead of thehafnium silicon oxide film 101 a, is formed near the surface of thesubstrate 100.

Then, a resist pattern 103 for forming the gate electrode structure isformed on the polysilicon film 102, as illustrated in FIG. 1(b), afterwhich the polysilicon film 102 is patterned by dry etching using achlorine gas, for example, while using the resist pattern 103 as a mask,as illustrated in FIG. 1(c). Thus, a gate electrode 104 made of thepolysilicon film 102 is formed. The dry etching process is stopped at acertain point in the gate insulating film having a layered structureincluding the hafnium oxide film 101 b and the hafnium silicon oxidefilm 101 a, specifically, when the hafnium oxide film 101 b is removedand the hafnium silicon oxide film 101 a is exposed in a portion of thegate insulating film outside the gate electrode 104.

Note that in the present embodiment, the dry etching process illustratedin FIG. 1(c) may be stopped when the polysilicon film 102 is removed andthe hafnium oxide film 101 b is exposed, may be stopped when the hafniumoxide film 101 b is partially removed, or may be stopped when thehafnium oxide film 101 b is removed and the hafnium silicon oxide film101 a is partially removed. Note however that the etching process mustbe stopped before the substrate 100 is exposed. This is because when thesubstrate 100, i.e., a silicon substrate, is exposed to a chlorine gas,which is the etching gas, the silicon substrate is etched significantlyby the chlorine gas.

Then, as illustrated in FIG. 1(d), the resist pattern 103 is removed byashing, after which a portion of the hafnium silicon oxide film 101 aoutside the gate electrode 104 is removed and a portion of the substrate100 outside the gate electrode 104 is exposed by wet etching using anaqueous hydrogen fluoride solution, for example. Thus, a gate electrodestructure is produced. Note that the wet etching step illustrated inFIG. 1(d) will later be described in detail.

Finally, although not shown in the figures, a source region and a drainregion are formed in the substrate 100 by using an ion implantationmethod, for example, thereby completing a field-effect transistor inwhich a hafnium oxide film, being a high-k material film, is used as thegate insulating film.

A method for removing a hafnium silicon oxide film by wet etching usingan aqueous hydrogen fluoride solution, as illustrated in FIG. 1(d), willnow be described in detail.

FIG. 2 is a schematic diagram illustrating a configuration of an etchingapparatus of the present embodiment, specifically, a wet etchingapparatus including an ultraviolet light radiation mechanism.

As illustrated in FIG. 2, the substrate 100 is placed on a substratetable 201. Note that the hafnium silicon oxide film 101 a, or the like,being an etching object on the substrate 100 is not shown in the figure.A rotating shaft (rotating mechanism) 201 a for spinning the substratetable 201 is attached to the lower surface of the substrate table 201,whereby the substrate 100 can be spun together with the substrate table201. Moreover, an excimer lamp 202 is provided above the substrate 100placed on the substrate table 201 as an ultraviolet light source(illumination mechanism). The excimer lamp 202 radiates xenon excimer(Xe Excimer) light 203 having a wavelength of 172 nm. Note that while alamp that radiates light having a different wavelength, such as F₂laser, may be used instead of the excimer lamp 202, the excimer lamp 202radiating the xenon excimer light 203 having a wavelength of 172 nm isused in the present embodiment in view of the efficiency at which ozoneis generated by the ultraviolet light irradiation and the transmissivityof the lamp light through the atmosphere.

Moreover, as illustrated in FIG. 2, the etching apparatus of the presentembodiment includes a gas supply section 204 capable of supplying aninert gas such as a nitrogen gas, for example, into the space betweenthe substrate 100 on the substrate table 201 and the excimer lamp 202,and also includes a chemical liquid supply section 205 capable ofsupplying an etchant (chemical liquid) onto the substrate 100 on thesubstrate table 201. Note that the wet etching apparatus of the presentembodiment is an apparatus of a so-called “single wafer process” typethat processes one wafer to be the substrate 100 at a time.

Next, oxidation of the hafnium silicon oxide film by ultraviolet light(UV light) radiated from the excimer lamp 202 will be described. Asdescribed above with reference to FIG. 1(c), at the time when the gateelectrode material (the polysilicon film 102) is patterned by dryetching into the gate electrode 104, the hafnium silicon oxide film 101a, i.e., a hafnium silicate (HfSi_(x)O_(y): x>0, y>0), is exposed on thesurface of the substrate 100 near the gate electrode 104. As describedabove in “Problems to be Solved by the Invention”, it is difficult toremove the insufficiently-oxidized hafnium silicon oxide film 101 a bywet etching using a solution of hydrogen fluoride, or the like.

In view of this, in the present embodiment, the xenon excimer light 203,which is ultraviolet light, is radiated from the excimer lamp 202 towardthe substrate 100 in an oxygen-containing atmosphere by using theetching apparatus illustrated in FIG. 2. Thus, ozone is generated in theatmosphere, and an insufficiently-oxidized hafnium silicate (the hafniumsilicon oxide film 101 a) on the substrate 100 is oxidized by the ozone,starting from its surface side. In this process, similar effects can beobtained by using ultraviolet light other than the xenon excimer light203.

Moreover, when radiating the xenon excimer light 203 in the presentembodiment, a nitrogen gas, for example, is supplied from the gas supplysection 204 into the space between the substrate 100 on the substratetable 201 and the excimer lamp 202 in order to suppress the attenuationof the xenon excimer light 203, i.e., ultraviolet light, in the space.Note that the 50% attenuation length of the xenon excimer light 203having a wavelength of 172 nm in the air is 5 mm. Moreover, the supplyof a nitrogen gas from the gas supply section 204 is provided so thatthe space between the substrate 100 on the substrate table 201 and theexcimer lamp 202 is not filled solely with the nitrogen gas, or in otherwords so that oxygen atoms, which are the source of ozone, are not alleliminated from the space. Note that the minimum oxygen concentrationrequired for ozone generation is on the order of ppm.

Specifically, in the wet etching step illustrated in FIG. 1(d), i.e.,the etching step of the present embodiment, first, the xenon excimerlight 203 (UV light) is radiated from the excimer lamp 202 toward thesubstrate 100 on the substrate table 201 for about 60 seconds whilesupplying a nitrogen gas from the gas supply section 204. Then, anaqueous hydrogen fluoride solution, for example, is supplied from thechemical liquid supply section 205 toward the substrate 100 on thesubstrate table 201, thereby wet-etching the hafnium silicate(specifically, a portion of the hafnium silicon oxide film 110 a outsidethe gate electrode 104). In this process, the aqueous hydrogen fluoridesolution can be supplied uniformly onto the substrate 100 by spinningthe substrate 100 together with the substrate table 201 by the rotatingshaft 201 a.

In this way, the hafnium silicate, which is normally insoluble in anaqueous hydrogen fluoride solution, becomes soluble in an aqueoushydrogen fluoride solution by the UV light irradiation. This is for thefollowing reason. That is, oxygen in the atmosphere is turned into ozoneby the UV light irradiation, and a surface portion of theinsufficiently-oxidized hafnium silicate is oxidized by the ozone. As aresult, the surface portion of the hafnium silicate takes astoichiometric composition close to that of hafnium oxide, whereby thesurface portion is dissolved in the aqueous hydrogen fluoride solution.

Note that in a case where the hafnium silicate film has such a largethickness that the film cannot entirely be removed by a single iterationof the UV light irradiation and the hydrogen fluoride treatment, the setof processes including the UV light irradiation and the hydrogenfluoride treatment is repeated for the film. Specifically, theinsufficiently-oxidized hafnium silicate on the substrate is oxidized bythe UV light irradiation, and then the oxidized hafnium silicate isremoved by the hydrogen fluoride treatment. Then, after hydrogenfluoride remaining on the substrate is washed away with pure water, thesurface condition of the substrate is measured by, for example,confirming the water repellency of the substrate. If it is confirmedthat the surface of the substrate (silicon substrate) is not exposed,the second set of the UV light irradiation and the hydrogen fluoridetreatment is performed for the hafnium silicate remaining on thesubstrate, thus removing the newly-oxidized hafnium silicate. Then,after hydrogen fluoride remaining on the substrate is washed away withpure water, the surface condition of the substrate is measured again.Thus, the set of processes is repeated until it is confirmed by themeasurement that the substrate surface is exposed, specifically, untilthe water repellency of the substrate surface is confirmed. In such acase, in order to improve the throughput in the manufacture of asemiconductor device, it is preferred that the washing with pure waterand the measurement of the substrate surface condition can be performedin the same apparatus that performs the UV light irradiation and thehydrogen fluoride treatment (e.g., the etching apparatus illustrated inFIG. 2).

As described above, according to the present embodiment, the process ofetching the gate insulating film having the hafnium silicon oxide film(silicate layer) 101 a is performed by oxidizing theinsufficiently-oxidized hafnium silicon oxide film 101 a and thenwet-etching the oxidized hafnium silicon oxide film 101 a. In thisprocess, the composition of the oxidized hafnium silicon oxide film 101a comes closer to the stoichiometric composition of hafnium oxide. Thus,the oxidized hafnium silicon oxide film 101 a becomes more soluble in anetchant such as an aqueous hydrogen fluoride solution, for example.Therefore, it is possible to reliably remove the oxidized hafniumsilicon oxide film 101 a by wet etching, and to prevent a situationwhere impurities remain between gate electrode structures, therebyimproving the production yield in the manufacture of a semiconductordevice.

Moreover, according to the first embodiment, an aqueous hydrogenfluoride solution that does not substantially etch the substrate(silicon substrate) 100 underlying the gate insulating film is used asthe etchant, whereby the oxidized hafnium silicon oxide film 101 a canbe removed selectively by wet etching.

Moreover, according to the first embodiment, the xenon excimer light203, which is ultraviolet light, is radiated from the excimer lamp 202toward the substrate 100 in an oxygen-containing atmosphere by using theetching apparatus illustrated in FIG. 2. Therefore, it is possible toreliably oxidize the hafnium silicon oxide film 101 a on the substrate100 by the ozone generated in the atmosphere. Moreover, the oxidizationof the hafnium silicon oxide film 101 a is performed in a gaseous phase.Therefore, even if the wafer to be the substrate 100 has surfaceirregularities, the hafnium silicon oxide film 101 a can be oxidizedmore uniformly, as compared with wet oxidization. Specifically, even ifthe wafer has minute surface irregularities, the hafnium silicon oxidefilm 101 a can be etched uniformly by performing the hydrogen fluoridetreatment after it is irradiated with the xenon excimer light 203, i.e.,UV light, thereby improving the production yield in the manufacture of asemiconductor device.

Note that in the first embodiment, when the hafnium silicon oxide film101 a is removed by wet etching, the UV light irradiation and thehydrogen fluoride treatment are performed separately. Alternatively, theUV light irradiation and the hydrogen fluoride treatment may beperformed together. Specifically, an aqueous hydrogen fluoride solutionis supplied from the chemical liquid supply section 205 onto thesubstrate 100 while supplying a nitrogen gas from the gas supply section204 into the space between the substrate 100 on the substrate table 201and the excimer lamp 202, by using the etching apparatus illustrated inFIG. 2. In this process, the xenon excimer light 203 is radiated fromthe excimer lamp 202 toward the substrate 100 at the same time. In thisway, a portion of the insufficiently-oxidized hafnium silicon oxide film101 a (i.e., a hafnium silicate) that has been oxidized by the UV lightirradiation is dissolved in the aqueous hydrogen fluoride solution,whereby the hafnium silicate outside the gate electrode 104 iseventually removed so that the substrate 100, i.e., the silicon region,is exposed.

Moreover, in the first embodiment, the hafnium silicon oxide film 101 a,which is the lower-layer portion of the gate insulating film, is removedby the UV light irradiation and the hydrogen fluoride treatment afterremoving the hafnium oxide film 101 b, which is the upper-layer portionof the gate insulating film. Alternatively, the hafnium oxide film 101 bmay be removed by the UV light irradiation and the hydrogen fluoridetreatment. That is, it may not be necessary to wait for the hafniumsilicon oxide film 101 a to be exposed before performing the UV lightirradiation and the hydrogen fluoride treatment to remove the hafniumsilicon oxide film 101 a. In other words, the UV light irradiation andthe hydrogen fluoride treatment may be initiated to remove the hafniumoxide film 101 b when the polysilicon film 102 is removed and thehafnium oxide film 101 b is exposed. This is because the hafnium oxidefilm 101 b can of course be removed by the UV light irradiation and thehydrogen fluoride treatment. Note that where the hafnium oxide film 101b has been crystallized through a high-temperature heat treatment, orthe like, it is preferred to use an aqueous hydrogen fluoride solutionhaving a concentration (by volume) of about 10% and a temperature ofabout 70° C. for removing the hafnium oxide film 101 b.

Moreover, in the first embodiment, an aqueous hydrogen fluoride solutionas an etchant is supplied in an ordinary liquid state when etching awaythe hafnium silicon oxide film 101 a after the UV light irradiation.Alternatively, hydrogen fluoride may be supplied in a gaseous state.That is, an anhydrous hydrogen fluoride vapor may be used. Moreover,other than an aqueous hydrogen fluoride solution, the etchant may beanother liquid containing fluorine and hydrogen, a phosphoric acidsolution, or the like.

Moreover, while an etching object is irradiated with ultraviolet lightin an oxygen-containing atmosphere in the first embodiment, similareffects can be obtained by irradiating the etching object withultraviolet light while an oxygen-containing liquid (e.g., water) isattached to the surface of the etching object.

Moreover, while the present invention is applied to the removal of asilicate compound on the surface side of a wafer in the firstembodiment, the present invention may alternatively be applied to theremoval of a silicate compound on the reverse side of a wafer. In such acase, it is possible to prevent the cross-contamination between wafersbeing processed.

Variation of First Embodiment

A method for manufacturing a semiconductor device according to avariation of the first embodiment of the present invention will now bedescribed with reference to the drawings.

The present variation differs from the first embodiment only in themethod for removing a hafnium silicon oxide film by wet etching using anaqueous hydrogen fluoride solution (see FIG. 1(d)). Specifically, in thefirst embodiment, the hafnium silicon oxide film is oxidized by usingthe ozone generated by the UV light radiation (radiation of the xenonexcimer light 203) before performing the hydrogen fluoride treatment onthe insufficiently-oxidized hafnium silicon oxide film. In contrast, inthe present variation, a hafnium silicon oxide film (hafnium silicate)is oxidized by using ozone water before performing the hydrogen fluoridetreatment on an insufficiently-oxidized hafnium silicon oxide film.

FIG. 3 is a schematic diagram illustrating a configuration of an etchingapparatus according to the present variation.

As illustrated in FIG. 3, the substrate 100 is placed on a substratetable 201. Note that the hafnium silicon oxide film 101 a, or the like,being an etching object on the substrate 100 is not shown in the figure.The rotating shaft (rotating mechanism) 201 a for spinning the substratetable 201 is attached to the lower surface of the substrate table 201,whereby the substrate 100 can be spun together with the substrate table201. Moreover, the etching apparatus of the present variation includesthe chemical liquid supply section 205 capable of supplying an etchant(chemical liquid) onto the substrate 100 on the substrate table 201, andalso includes an ozone water supply section 206 capable of supplyingozone water onto the substrate 100. Note that the wet etching apparatusof the present variation is an apparatus of a so-called “single waferprocess” type that processes one wafer to be the substrate 100 at atime.

In the present variation, first, ozone water is supplied from the ozonewater supply section 206 onto the substrate 100 while spinning thesubstrate 100 together with the substrate table 201 by the rotatingshaft 201 a, by using the etching apparatus illustrated in FIG. 3. Inthis way, the insufficiently-oxidized hafnium silicate (the hafniumsilicon oxide film 101 a) on the substrate 100 is oxidized.

Next, the substrate 100 is spun by using the rotating shaft 201 a toshake the ozone water off the substrate 100. Then, an aqueous hydrogenfluoride solution, for example, is supplied from the chemical liquidsupply section 205 toward the substrate 100, again while spinning thesubstrate 100. In this way, a portion of the insufficiently-oxidizedhafnium silicate, which is normally insoluble in an aqueous hydrogenfluoride solution, that has been oxidized by the ozone water treatmenttakes a stoichiometric composition close to that of hafnium oxide,whereby the portion is reliably dissolved in the aqueous hydrogenfluoride solution. Thus, a portion of the hafnium silicon oxide film 101a outside the gate electrode 104 is reliably removed by wet etching.

Note that in a case where the hafnium silicate film has such a largethickness that the film cannot entirely be removed by a single iterationof the ozone water treatment and the hydrogen fluoride treatment, theset of processes including the ozone water treatment and the hydrogenfluoride treatment is repeated for the film. Specifically, the hafniumsilicate on the substrate is oxidized by the ozone water treatment, andthen the oxidized hafnium silicate is removed by the hydrogen fluoridetreatment. Then, after hydrogen fluoride remaining on the substrate iswashed away with pure water, the surface condition of the substrate ismeasured by, for example, confirming the water repellency of thesubstrate. If it is confirmed that the surface of the substrate (siliconsubstrate) is not exposed, the second set of the ozone water treatmentand the hydrogen fluoride treatment is performed for the hafniumsilicate remaining on the substrate, thus removing the newly-oxidizedhafnium silicate. Then, after hydrogen fluoride remaining on thesubstrate is washed away with pure water, the surface condition (waterrepellency) of the substrate is confirmed again. Thus, the set ofprocesses is repeated until it is confirmed by the measurement that thesubstrate surface is exposed. In such a case, in order to improve thethroughput in the manufacture of a semiconductor device, it is preferredthat the washing with pure water and the measurement of the substratesurface condition can be performed in the same apparatus that performsthe ozone water treatment and the hydrogen fluoride treatment (e.g., theetching apparatus illustrated in FIG. 3).

As described above, according to the present variation, the process ofetching the gate insulating film having the hafnium silicon oxide film(silicate layer) 101 a is performed by oxidizing theinsufficiently-oxidized hafnium silicon oxide film 101 a and thenwet-etching the oxidized hafnium silicon oxide film 101 a. In thisprocess, the composition of the oxidized hafnium silicon oxide film 101a comes closer to the stoichiometric composition of hafnium oxide. Thus,the oxidized hafnium silicon oxide film 101 a becomes more soluble in anetchant such as an aqueous hydrogen fluoride solution, for example.Therefore, it is possible to reliably remove the oxidized hafniumsilicon oxide film 101 a by wet etching, and to prevent a situationwhere impurities remain between gate electrode structures, therebyimproving the production yield in the manufacture of a semiconductordevice.

Moreover, according to the present variation, an aqueous hydrogenfluoride solution that does not substantially etch the substrate(silicon substrate) 100 underlying the gate insulating film is used asthe etchant, whereby the oxidized hafnium silicon oxide film 101 a canbe removed selectively by wet etching, and the etching can be stopped atthe surface of the substrate 100. Thus, the surface of the substrate 100(a portion outside the gate electrode 104) can be exposed withoutetching the surface of the substrate 100.

Moreover, according to the present variation, ozone water is suppliedfrom the ozone water supply section 206 onto the substrate 100 by usingthe etching apparatus illustrated in FIG. 3. Therefore, the hafniumsilicon oxide film 101 a on the substrate 100 can reliably be oxidizedby the ozone water.

Note that when ozone water is supplied from the ozone water supplysection 206 onto the substrate 100 in the present variation, thesubstrate 100 may be irradiated with UV light by using an ultravioletlight source, e.g., the excimer lamp 202 in the etching apparatus of thefirst embodiment illustrated in FIG. 2.

Moreover, in the present variation, the hafnium silicon oxide film 101a, which is the lower-layer portion of the gate insulating film, isremoved by the ozone water treatment and the hydrogen fluoride treatmentafter removing the hafnium oxide film 101 b, which is the upper-layerportion of the gate insulating film. Alternatively, the hafnium oxidefilm 101 b may be removed by the ozone water treatment and the hydrogenfluoride treatment. That is, it may not be necessary to wait for thehafnium silicon oxide film 101 a to be exposed before performing theozone water treatment and the hydrogen fluoride treatment to remove thehafnium silicon oxide film 101 a. In other words, the ozone watertreatment and the hydrogen fluoride treatment may be initiated to removethe hafnium oxide film 101 b when the polysilicon film 102 is removedand the hafnium oxide film 101 b is exposed. This is because the hafniumoxide film 101 b can of course be removed by the ozone water treatmentand the hydrogen fluoride treatment. Note that where the hafnium oxidefilm 101 b has been crystallized through a high-temperature heattreatment, or the like, it is preferred to use an aqueous hydrogenfluoride solution having a concentration (by volume) of about 10% and atemperature of about 70° C. for removing the hafnium oxide film 101 b.

Moreover, in the present variation, an aqueous hydrogen fluoridesolution as an etchant is supplied in an ordinary liquid state whenetching away the hafnium silicon oxide film 101 a after the ozone watertreatment. Alternatively, hydrogen fluoride may be supplied in a gaseousstate. That is, an anhydrous hydrogen fluoride vapor may be used.Moreover, other than an aqueous hydrogen fluoride solution, the etchantmay be another liquid containing fluorine and hydrogen, a phosphoricacid solution, or the like. Moreover, while ozone water is used foroxidizing the hafnium silicon oxide film 101 a, another ozone-containingliquid may alternatively be used.

Moreover, the present invention is applied to the removal of a silicatecompound on the surface side of a wafer in the present variation.Alternatively, the present invention may be applied to the removal of asilicate compound on the reverse side of a wafer. In such a case, it ispossible to prevent the cross-contamination between wafers beingprocessed.

Evaluation of First Embodiment and Variation Thereof

The results of the experimental evaluation of the first embodiment andthe variation thereof will now be described.

The present inventor removed a hafnium silicate in the following threeprocess methods in order to evaluate the first embodiment and thevariation thereof

-   -   (1) Combination of the UV light irradiation in an        oxygen-containing atmosphere and the hydrogen fluoride treatment        (corresponding to the first embodiment; hereinafter referred to        as the “UV/DHF process”)    -   (2) Combination of the ozone water treatment and the hydrogen        fluoride treatment (corresponding to the variation of the first        embodiment; hereinafter referred to as the “O₃/DHF process”)    -   (3) The hydrogen fluoride treatment alone (comparative example;        hereinafter referred to as the “DHF process”)

Specifically, each of processes (1) to (3) was regarded as one cycle andrepeated to wet-etch the hafnium silicate. Note that for the DHF process(process (3)), the DHF process alone constitutes one cycle.

Moreover, the detailed conditions of processes (1) to (3) are asfollows.

-   -   (1) The UV light irradiation was performed for 60 seconds using        xenon excimer light, and a treatment with an aqueous hydrogen        fluoride solution having a concentration (by volume;        concentration hereinafter refers to a concentration by volume)        of 2.5% was performed for 30 seconds.    -   (2) The ozone water treatment (ozone washing) was performed for        60 seconds, and a treatment with an aqueous hydrogen fluoride        solution having a concentration of 2.5% was performed for 30        seconds.    -   (3) A treatment with an aqueous hydrogen fluoride solution        having a concentration of 2.5% was performed for 30 seconds.

As hafnium silicate on a silicon substrate was removed under theconditions above, the silicon substrate was exposed and the waterrepellency was confirmed in the fourth cycle for the UV/DHF process(process (I)) and the O₃/DHF process (process (2)). On the other hand,the water repellency was not confirmed when the DHF process (process(3)) alone was performed.

Thus, a hafnium silicate (HfSi_(x)O_(y): x>0, y>0) present on thesubstrate surface cannot be etched substantially by the DHF processalone. In contrast, oxidizing the hafnium silicate by the UV lightirradiation or the ozone water treatment facilitates the etching of thehafnium silicate by the hydrogen fluoride treatment. The reason for thiswas believed to be as follows based on XPS (X-ray PhotoelectronSpectroscopy).

FIG. 4 shows the results of XPS on the state of chemical bond on thesurface of each sample (hafnium silicate) prepared through a differentprocess, specifically, the results obtained from Hf (hafnium) 4f XPSspectra. Generally, with XPS, it is possible to know the state ofchemical bond (the state of oxidation in the present invention) based onthe amount of shift in the 4f 7/2 peak.

In FIG. 4, the result “a” is based on an Hf 4 f (the right peak: 4f 7/2,the left peak: 4f 5/2) XPS spectrum obtained by measuring the surface ofa hafnium silicate layer having a thickness of 3.5 nm deposited by a CVDmethod (deposition temperature: 450° C.) in an unprocessed state.Moreover, the result “b” is based on an Hf 4f XPS spectrum obtained bymeasuring the surface of the same hafnium silicate layer but afterperforming the UV light irradiation for 60 seconds. Moreover, the result“c” is based on an Hf 4f XPS spectrum obtained by measuring the surfaceof the same hafnium silicate layer but after performing the ozone watertreatment for 60 seconds. Furthermore, the result “d” is based on an Hf4f XPS spectrum obtained by measuring the surface of the same hafniumsilicate layer but after treating the layer with an aqueous hydrogenfluoride solution having a concentration of 2.5% for 30 seconds.

As illustrated in FIG. 4, the result “b” (UV light irradiation) and theresult “c” (ozone water treatment) give higher XPS spectrum values thanthose of the result “a” (unprocessed) and the result “d” (2.5% DHFprocess). This indicates more advanced states of oxidation of Hf atomsfor the result “b” (UV light irradiation) and the result “c” (ozonewater treatment). Thus, it was confirmed that theinsufficiently-oxidized hafnium silicate was oxidized by the UV lightirradiation or the ozone water treatment. Therefore, as described abovein the first embodiment and the variation thereof, etching of aninsufficiently-oxidized hafnium silicate, which is normally insoluble inan aqueous hydrogen fluoride solution, is facilitated by performing thehydrogen fluoride treatment in combination with the UV light irradiationor the ozone water treatment.

Second Embodiment

A compound analysis method according to the second embodiment of thepresent invention, specifically, a method for analyzing a silicatecompound that is formed on the substrate surface when a hafnium oxidefilm is used as the gate insulating film. Note that in the compoundanalysis method of the present embodiment, the silicate compound isdissolved and removed by using the etching method of the firstembodiment or the variation thereof, while the used etchant (chemicalliquid) is collected, and the composition of the collected chemicalliquid is analyzed. A quantitative analysis such as a high-frequencyinductively-coupled plasma mass analysis, for example, is performed asthe compositional analysis of the chemical liquid.

FIG. 5 is a flow chart illustrating the compound analysis methodaccording to the second embodiment.

First, in step S1, a substrate on which a silicate (e.g., the hafniumsilicon oxide film) is formed is prepared. FIG. 6 illustrates an exampleof a cross section of such a substrate. Specifically, aninsufficiently-oxidized hafnium silicon oxide film 151 is formed on asubstrate 150 made of silicon, for example, as illustrated in FIG. 6.Alternatively, a substrate having a cross section as illustrated in FIG.1(c) of the first embodiment may be prepared.

Then, in step S2, the insufficiently-oxidized hafnium silicon oxide film151 is oxidized by using the UV light irradiation of the firstembodiment or the ozone water treatment of the variation of the firstembodiment. Then, in step S3, the oxidized hafnium silicon oxide film151 is removed by wet etching using a hydrogen fluoride (DHF) solution.

Then, in step S4, it is confirmed whether or not the surface of thesubstrate 150 exhibits water repellency. If the surface of the substrate150 exhibits water repellency, it is determined that the surface of thesubstrate 150 is exposed, and the etching process is stopped.Specifically, the UV light irradiation or the ozone water treatment andthe following hydrogen fluoride treatment are stopped. On the otherhand, if the surface of the substrate 150 does not exhibit waterrepellency, it is determined that the surface of the substrate 150 isnot yet exposed, and the etching process is continued. Specifically, theprocess goes back to step S2 to again perform the set of processesincluding the UV light irradiation or the ozone water treatment and thehydrogen fluoride treatment.

As described above, in the present embodiment, the set of processesdescribed above is repeated until the surface of the substrate 150 isexposed, and the used chemical liquid (hereinafter referred to as the“waste liquid”) is collected. Specifically, where the etching method ofthe first embodiment is used, the waste liquid produced by successivelyperforming the UV light irradiation and the hydrogen fluoride treatmentis collected. Where the etching method of the variation of the firstembodiment is used, the waste liquid produced by successively performingthe ozone water treatment and the hydrogen fluoride treatment iscollected. In such a case, the ozone water may be collected togetherwith the aqueous hydrogen fluoride solution, or the aqueous hydrogenfluoride solution alone may be collected.

Finally, in step S5, a mass analysis of the collected waste liquid isperformed by using a high-frequency inductively-coupled plasma massanalyzer, for example. In this way, it is possible to identify theimpurities contained in the hafnium silicon oxide film 151.

Thus, according to the second embodiment, the etching method of thefirst embodiment or the variation thereof is performed on the hafniumsilicon oxide film 151, after which the waste liquid is collected andanalyzed. Therefore, it is possible to reliably remove theinsufficiently-oxidized hafnium silicon oxide film 151, which isdifficult to remove by a conventional wet etching process, and it ispossible to easily identify the impurities contained in the hafniumsilicon oxide film 151 simply by analyzing the collected waste liquid(by a compositional analysis such as a mass analysis). Note that aninsufficiently-oxidized silicate compound such as a hafnium siliconoxide film is conventionally analyzed by dissolving a silicate compoundin a phosphoric acid or a fluoronitric acid (a mixed solution ofhydrogen fluoride and nitric acid), and then collecting and analyzingthe chemical liquid. However, this method has the following twoproblems. That is, where a silicate compound is formed on a siliconsubstrate, significant dissolution of the substrate by a phosphoricacid, a fluoronitric acid, or the like, is inevitable. Moreover,performing a mass analysis, or the like, on such a chemical liquidlowers the precision of the quantitative analysis. Therefore, thecompound analysis method of the present embodiment using the etchingmethod of the first embodiment or the variation thereof is very useful.

Variation of Second Embodiment

A compound analysis method according to the variation of the secondembodiment of the present invention, specifically, a method foranalyzing a silicate compound that is formed on the substrate surfacewhen a hafnium oxide film is used as the gate insulating film. Note thatalso in the compound analysis method of the present variation, theinsufficiently-oxidized silicate compound is dissolved and removed byusing the etching method of the first embodiment or the variationthereof, while the used etchant (chemical liquid) is collected, and thecomposition of the collected chemical liquid is analyzed. A quantitativeanalysis such as a high-frequency inductively-coupled plasma massanalysis, for example, is performed as the compositional analysis of thechemical liquid.

The present variation differs from the second embodiment as follows. Inthe second embodiment, a hafnium silicon oxide film is dissolved in anaqueous hydrogen fluoride solution, and the composition of the solutionis analyzed so as to directly identify the impurities in the hafniumsilicon oxide film. In contrast, in the present variation, theimpurities in a layered film of the hafnium silicon oxide film and thehafnium oxide film are identified while the impurities in the hafniumoxide film are identified, and the identification results are comparedwith each other, thereby indirectly identifying the impurities in thehafnium silicon oxide film.

Specifically, in the present variation, a first silicon substrate and asecond silicon substrate are prepared. A layered film (first layeredfilm) of a hafnium silicon oxide film (lower-layer film) and a hafniumoxide film (upper-layer film) is formed on the first silicon substrate,and a second layered film having the same structure as that of the firstlayered film is formed on the second silicon substrate. The first andsecond silicon substrates are formed simultaneously in the same step.FIG. 7 illustrates an example of a cross section of the first and secondsilicon substrates. As illustrated in FIG. 7, an insufficiently-oxidizedhafnium silicon oxide film 161 is formed on a substrate 160, and ahafnium oxide film 162 is formed on the hafnium silicon oxide film 161.

Then, the UV light irradiation of the first embodiment or the ozonewater treatment of the variation of the first embodiment and thefollowing hydrogen fluoride treatment are performed on the first siliconsubstrate to dissolve the hafnium silicon oxide film 161 and the hafniumoxide film 162 in an aqueous hydrogen fluoride solution, and the aqueoushydrogen fluoride solution is collected and subjected to a massanalysis. In this way, the impurities contained in the first layeredfilm including the hafnium silicon oxide film 161 and the hafnium oxidefilm 162 are identified. “HfO₂-1” in FIG. 8 shows the detected amount ofeach impurity thus identified. It can be seen from the data shown in“HfO₂-1” in FIG. 8 that the first layered film contains sodium (Na),iron (Fe), etc., in addition to hafnium. Note that the etching processfor the hafnium silicon oxide film 161 in the first layered film issimilar to steps S2 to S4 (the etching process for the hafnium siliconoxide film 151) of the second embodiment illustrated in FIG. 5.

Then, the hydrogen fluoride treatment, i.e., wet etching using anaqueous hydrogen fluoride solution, is performed on the second siliconsubstrate having formed thereon the second layered film, which issimilar in structure to the first layered film. In this process, theinsufficiently-oxidized hafnium oxide film 162 in the second layeredfilm is dissolved in the aqueous hydrogen fluoride solution, while thehafnium silicon oxide film 161 in the second layered film is notdissolved therein. Therefore, the impurities contained in the hafniumoxide film 162 are identified by collecting the waste liquid produced inthe hydrogen fluoride treatment and analyzing the collected waste liquidby using a mass analyzer, for example. “HfO₂-2” in FIG. 8 shows thedetected amount of each impurity thus identified. It can be seen fromthe data shown in “HfO₂-2” in FIG. 8 that the hafnium oxide film 162 inthe second layered film contains sodium (Na), etc., in addition tohafnium.

Finally, the data shown in “HfO₂-1” and the data shown in “HfO₂-2” inFIG. 8 are compared with each other, thereby indirectly identifying theimpurities contained in the hafnium silicon oxide film 161.

Note that the first embodiment or the variation thereof or the secondembodiment or the variation thereof has been described with respect tothe etching of a hafnium silicate (hafnium silicon oxide film). However,the present invention is not limited to this, and similar effects can beobtained also when the present invention is applied to the etching of azirconium silicate (ZrSi_(x)O_(y): x>0, y>0), for example. Specifically,similar effects can be obtained when the present invention is applied tothe etching of a silicate compound containing at least one of Hf, Zr,Al, Ti, V, Co, Ni, Cu, Ga, Sr, Y, Nb, Mo, Ru, Pd, La, Ta, W, Ir, Pr, Nd,etc. Moreover, similar effects can be obtained when the presentinvention is applied to the etching of an intermetallic compound(specifically, a compound between silicon and a metal, e.g., cobaltsilicide (CoSi)) containing at least one of Hf, Zr, Al, Ti, V, Co, Ni,Cu, Ga, Sr, Y, Nb, Mo, Ru, Pd, La, Ta, W, Ir, Pr, Nd, etc., instead of asilicate compound.

1-20. (canceled)
 21. A method for manufacturing a semiconductor device,comprising: a step of forming a gate insulating film on a siliconregion; a step of forming a conductive film on the gate insulating film;a step of forming a gate electrode by dry-etching the conductive filmusing a mask that covers a gate electrode formation region; and a stepof removing a portion of the gate insulating film outside the gateelectrode by wet etching, wherein: the gate insulating film includes aninsulating layer made of a compound containing a metal, silicon andoxygen; and the step of removing the gate insulating film includes astep of oxidizing the insulating layer and then removing the oxidizedinsulating layer by wet etching.
 22. The method for manufacturing asemiconductor device of 21, wherein: the metal is hafnium or zirconium;and a solution containing fluorine and hydrogen is used as an etchant inthe step of removing the insulating layer.
 23. The method formanufacturing a semiconductor device of 21, wherein: the gate insulatingfilm further includes an oxide film formed on the insulating layer andmade of an oxide of a metal of the same kind as the metal; and the stepof removing the gate insulating film includes a step of removing aportion of the oxide film outside the gate electrode by wet etchingbefore oxidizing the insulating layer. 24-25. (canceled)